The present invention relates to a planographic printing plate material to which a photothermographic material employing an organic silver salt is applied, and a method of preparing a printing plate therefrom.
A method of preparing a printing plate is known which comprises the steps of exposing a planographic printing plate material without an original and developing the exposed material. Of these, a planographic printing plate material prepared according to a silver complex diffusion transfer process (DTR) is well known, in which silver images formed are employed as ink receptive portions. There are, for example, a planographic printing plate material comprising a support and provided thereon, a silver halide emulsion layer, and a physical developing nucleus layer in that order as disclosed in Japanese Patent Publication No. 48-30562, and Japanese Patent O.P.I. Publication Nos. 53-9603, 53-21602, 54-103104 and 56-9750, and a planographic printing plate material comprising an aluminum plate having thereon a physical developing nucleus layer and a silver halide emulsion layer on the nucleus layer as disclosed in Japanese Patent O.P.I. Publication Nos. 5-216236, and 6-81194.
However, these planographic printing plate materials are processed with a liquid such as a developing solution, which produces waste liquid, and disposal of the waste liquid is time-consuming and increases cost. There is, further, the problem that a processor used stains.
As a method in which liquid waste is not produced, there is a method as disclosed in Japanese Patent O.P.I. Publication No. 11-84669 in which thermal development is carried out without employing a developing solution. Such a thermal development has defects in that provide poor printing reproduction of images such as small dots or thin lines.
In view of the above, the present invention has been made. An object of the invention is to provide a planographic printing plate material employing a thermal development process without producing a liquid waste, and providing excellent printing reproduction and a preparing method thereof.